I. Field of the Invention
The invention relates generally to the field circulatory support and, more specifically, to cannulas and related methods for use in cardiopulmonary bypass circuits and cardiopulmonary bypass graft procedures.
II. Discussion of the Prior Art
To perform bypass or grafting operations, many times the heart is stopped or significantly slowed by infusing chemicals (such as cardioplegia) into the patient's heart muscle or lowering the temperature of the heart. Additionally, the contractions of the patient's heart may be controlled utilizing other available technology, such as pacing electrodes. Prior to slowing or stopping the heart, the patient is placed on a cardiopulmonary bypass (CPB) circuit. Blood is withdrawn from the patient's heart, passed through a CPB circuit (generally comprising a blood pump, oxygenator, heat exchanger, and a blood filter) before being returned to the patient through a cannula which may be placed within the aorta. The cannulas that are placed within the patient generally range in size from 12 Fr. to 51 Fr., are generally tubular in shape, and may be reinforced with wire. Generally speaking, the cannula must be sufficiently small to permit insertion into the heart with minimal damage to the tissue, though it must be large enough to provide sufficient blood flow. In prior art systems where a blood pump is used to replace or assist the function of the heart, blood must be removed from the patient's vascular system, passed through a pump and returned to the patient's body through a second cannula. Present bypass techniques require many feet of flexible tubing to connect the components in which the blood must flow through. Having the blood in contact with such a large amount of foreign material requires that the blood be treated with a large volume of Heparin to prevent clotting. Also, the large priming volume causes the patient's blood to be diluted with a large amount of saline. This serves to thin the patient's blood and lowers the oxygenation abilities, white blood cell count and increases the blood clotting time. While this type of bypass circuit works well, it is nonetheless complicated and requires a considerable amount of setup time and must be managed and constantly monitored by a skilled technician.
Another drawback with the prior art that, if the surgeon desires to support both the right and left side of the heart (bi-ventricular support) independently without the use of an extracorporeal oxygenator, up to four cannulas need to be placed within the patient's circulatory system. With the addition of each cannula, further complications may arise. Placing multiple cannulas within the surgical field can cause clutter, thereby blocking access required to perform certain surgical procedures. Another danger associated with bi-ventricle support circuits is the possible formation of emboli in the patient's blood stream. If sufficiently high suction exists in the left atrium, air may be drawn from outside the heart through the insertion incision thereby forming an air emboli.
Presently there is a trend in the surgical arts toward performing beating heart surgery. In beating heart surgery, the patient's heart is slowed but not stopped. While performing beating heart coronary artery bypass graft (CABG), the oxygenator may be eliminated from the CPB circuit and the patient's lungs used to oxygenate the blood. Beating heart CABG has a number of advantages over stopped heart or full CPB CABG. Specific studies have shown that patients placed on full bypass experience neurological problems, including but not limited to: memory loss, speech impairment, impaired coordination, systemic inflammatory response, and other complications. Also, many patients are too weak and/or infirm to survive the physical stresses associated with full CPB CABG, particularly patients of advanced age.
Due to the recency of beating heart surgery, specific cannulation systems have not been developed for use in procedures such as beating heart CABG. The present invention addresses this void in the prior art.